Have never had problems with avast but suddenly appeared to be disabled yesterday and cant enable it through normal methods
How did you try to enable it?
Were there any error messages? If yes what were they?
Did you notice a slow down on you computer or any other behavior out of the ordinary?
I suggest a full computer on-line scanning:
BitDefender
ESET NOD32
F-Secure
For detection-only, not cleaning:
Kaspersky
Trendmicro housecall
What avast processes are running in Task Manager, they begin with ash or asw, see image ?
Is the avast ‘a’ icon still in the system tray ?
If so does it have a Red circle with a red bar over the top of it.